Method and apparatus for automatically conditioning a lap



Dec. 4, 1956 c, VQYTECH 2,772,521

METHOD AND APPARATUS FOR AUTOMATICALLY CONDITIONING A LAP Filed Dec. 18, 1953 2 Sheets-Sheet l m 5 w 1 y f?! 4, 1956 c. F. VOYTECH 2,772,521

METHOD AND APPARATUS FOR AUTOMATICALLY CONDITIONING A LAP 2e I 27 W MH B W w P" N ff mi. 22 m i la i Alli H L o 7 1 I7 29 Q749 NINA N153 .23 N1 $1M: 5' 76 y l L e 7 Q9 7 CIZLUZCSE i Zg E/L United States METHUD AND APRARATUS FDR AUTQDMATK- (IALLY CUNDHKUNHNG A LAP This invention relates to a method and apparatus for lapping articles, and particularly to the type of lapping method and apparatus wherein means are provided to condition the lap simultaneously with the lapping of articles thereon.

There has been proposed a lapping machine which employs a disc-shaped rotatable lap having an annular lapping surface on which the articles to be lapped are placed, said articles being disposed within the confines of heavy conditioning rings resting on the lap. The diameters of the rings are larger than the radial dimension of the lap and the rings are so located on the lap that they overhang both the inner and outer peripheries of the lapping surface. These rings are allowed to rotate freely about their own axes, but are not permitted to revolve with the lap. As the rings rotate, they cover all parts of the lap and remove any irregularities in the lap surface which may be produced therein by the articles being lapped.

' It has been found that the location of the rings radially of the lap determines whether they will wear the lap flat, convex or concave, and to this end, means are pro vided in the aforementioned structure to adjust the position of the conditioning rings to produce the desired contour. Due to the fact that the wearing of the lap is the result of the combined wear produced by the articles and by the rings, despite the predictability of the wearing effect produced by the rings, the wear produced by the articles is variable and hence it is necessary to check the lap surface frequently to determine whether the lap has deviated from the desired contour. If it should develop that the contour is not the one desired, an adjustment must be made of the position of the rings to correct the undesirable condition. Several adjustments may be necessary before the right position is found. This adjustment requires vigilanceto detect a need for it, and skill to determine the amount and kind to correct the condition.

One of the principal objects of this invention is to provide, in a lapping machine of the'type described above, method and apparatus for automatically maintaining the lap in any desired condition of contour, said apparatus being'simple and inexpensive to construct and to install in such machines.

Another object of this invention is to provide a method of automatically conditioning a rotating lapping surface bya continuous comparison of the lapping surface with points on a standard surface having the desired contour.

Afurther object of this invention is the provision of an'automatic means for maintaining a lap in a predetermined condition as to contour, said means including conditioning rings rotating about fixed axes and used simultaneously with the lapping of articles, and said means beingadapted to change the wear of the lap by the rings by automatically controlling the relative pressure exerted by the rings radially of the lap so that when it is desired to produce a convexlap, greater pressure is exerted on the portion of the rings disposed over the radialatent ly outer region of the lap surface and to produ ce aconice cave lap, greater pressure is exerted on the portion of the rings disposed over the radially inner region of the lap surface.

As a more specific object, this invention contemplates the provision of an automatic means for maintaining a predetermined contour on a rotatable lap by means of conditioning rings which are fixed radially of the lap, said means comprising a relatively rigid weighted bar which spans the lap and rests upon conditioning rings the centers of which are on a diameter of the lap, the points of contact of the bar with the rings being adjustable so that the weight of the bar is taken on the portions of the rings disposed over the radially inner or outer regions or on both said regions, of the lap, depending upon whether the lap is to be concave, convex or flat.

As another specific object, this invention seeks to provide a lapping machine using conditioning rings for continuously creating or maintaining the lapping surface thereof in accordance with a predetermined contour, and a superstructure which holds the rings in place on the lap and at the same time exerts pressure upon the rings in a manner to wear the lap in accordance with the predetermined contour.

A feature of this invention is an adjustable bearing point for a weight applied to a rotatable conditioning ring for a lapping machine, said bearing point being graduated to facilitate the adjustment of the weight.

Another feature of this invention is an antifriction support for a weight on a rotating conditioning ring for a lapping machine which permits the application of a non-rotating weight to the rotating conditioning ring to provide the minimum resistance to the free rotation of the ring.

These and other objects and features of this invention will become apparent from the following description when taken together with the accompanying drawings in which:

Fig. 1 is a plan vieW of a lapping machine of the type to which this invention is applicable;

Fig. 2 is an enlarged fragmentary plan view of the lapping machine of Fig. 1;

Fig. 3 is a cross sectional view through the rings and weights of the lapping machine taken along the line 3-3 of Fig. 2; and

Figs. 4 to 7 show schematically the principle of operation of this invention.

Referring briefly to Fig. l, the type of lapping machine to which this invention is particularly adaptable is comprised of a stationary base or frame in on which is mounted for rotation about a vertical axis a circular lap iii, the upper surface of which is annular and adapted to be rotated under the article to be lapped to produce thereon a smooth surface of predetermined contour. Surface l2 may be fiat or it may be convex or concave.

The articles to be lapped are shown for purposes of illustration as discs 13. it is understood that this iJ- vention is not limited in its application to the lapping of discs, nor to the lapping of a single article at a time, such techniques as have been developed for the lapping of various articles on this type of lapping machine being usable with this invention. The discs 13 are placed within the confines of rings M (Fig. 3) which rest upon annular lap surface .12 and are held against revolution therewith by a means hereinafter to be described. The relative rotation of the lap surface past rings 14 induces rotation of said rings about their own axes. Articles 13, being also held against revolution with lap surface 12, will likewise rotate about their own axes.

The rotation of rings lid on lap surface 12 causes all parts of the surface contacted by the rings to be worn thereby, and by designing the Wear occasioned by the rings to be at least equal in depth to the wear occasioned by the articles, the rings will maintain the lap surface 12 in its original condition indefinitely. It will be noted that rings 14 overlap both the inner and outer peripheries, 15and 16, respectively, .of the lap surface 12. This insures complete coverage of the surface by the rings. In prior lapping machines of this type, the relative degree of overlap at the inner and outer peripheries is used to regulate the relative amount of wear between the inner and outer regions of the lap surface. Thus, it the overlap at the inner periphery is greater than at the outer periphery, a greater portion of the weight of the rings isborne by the inner regions as compared with the outer regions and hence the Wear at the inner regions is greater and the lap surface becomes concave. if the overlap at the outer periphery is greater, the lap surfacebecomes convex. By shifting the rings radially of the lap, one may control the contour of the lap. T his method of control, however, requires constant vigilance and some skill since there is no automatic means in such prior machines for shifting the rings to correct for a wear conditionwhich is not desired.

In the present invention, use is made of the principle in the lapping art according to which increased lapping effect can be made to take place over any selected area of'an article merely by causing an increase in the pressure exerted upon the article over that area. .ln the case of-the rings, increased wear over a selected annular area of the lapping surface can be effected when the pressure exerted by the ring over that area is increased. As the ring rotates, however, and the pressure must be exerted by a weight the radial position of which must be fixed over the area of the lap surface to be worn down, the

Weight must slide relative to the ring as the ring rotates under it.

Thus, one way to control the contour of the lap surface would be to provide variable pressure means for each ring, there being tWo such means for each ring, one located on the ring over the radial inner region of the lap surface and the other located on the ring over the radial outer region of the lap surface, the pressure exerted by each means being individually adjusted to produce the desired wear pattern. This method, however, requires constant checking and is no more automatic than the radial shifting method now in use.

According to the present invention, the pressure means is automatically adjusted very simply, for example, by a weight placed across two diametrically opposed rings so that both rings are affected by the weight. One convenient form of weight (for a flat lap surface) may be a bar of cast iron which has a perfectly flat surface resting on the rings and is symmetrically formed and located relative to the center of the lap. If the rings are of identical height, the bar will contact both the inner and outer regions of each ring when the lap surface is flat. If the lap surface is not flat, but concave, for example, and it is desired to restore it to a flat condition, the bar will contact only the outer regions of the rings and hence will cause the rings to wear the outer regions of the lap surface at a greater rate than the inner regions until the surface is flat. At that point, the bar will rest upon both the inner and outer regions and cause equal wear on both regions. If the lap sur face is convex, the bar will contact only the inner regions of the rings, increasing the Wear at the inner region of the lap surface until the lap surface is flat.

The principle of this invention is illustrated in Figs. 4 to 7. In Fig. 4, the lap 11 is mounted on a rotatable shaft 17 and has a flat annular lap surface 18 on which are placed two conditioning rings 19 and 20 of equal height. Each ring has an outside diameter which is greater than the radial dimension of the lap surface 13 so that each ring overlaps both the inner periphery 15 and outer periphery 16 of surface 18. The amount of overlap in this case is selected only to produce wear over the entire lap surface.

Across both rings is placed a heavy weight in the form of a bar 21 having four contact points 22, 23, 24 and 25 which may be the rounded ends of screws or bolts extending through said bar. Assuming that it is desired to maintain lap surface 16 in its flat condition, and assuming that the top surfaces 26 and 27 of the rings 19 and 20 are parallel with their bottom surfaces 28 and 29, contact points 22, 23, 24 and 25 will be made to lie in a straight line. This distributes the weight of the her among the four contact points, and the wear of the lap by rings 19 and 20 will therefore be along a fiat plane and the flat surface will be maintained indefinitely.

If for any reason, the inner region of the lap surface should be W01'1'l more than the outer. region so as to produce a concave condition such as is shown at *30 in tacts 22'and 25 and decreasingor entirely removing-the weight from the inner contacts 23 and 24. .This increases the wear on the outer regions of the lap surface Bfland;

decreases the wear on the inner regions, which ultimately results. in a flat lap surface. As soon as the lap surface is.

flat, contact will be restored between the inner points 2 3 and 24 and their respective ring surfaces 26 and 27, and. thereafter, the wear will be even and the lap surface will.

remain flat.

The application of this invention to a convex lap surface 31 is shown in Fig. 6. This i the reverse of the con dition shown in Fig. 5 and entails the relief of pressure on'the outer contacts 22and 2'5 and an increase in pressure on the inner contacts 23 and 24. When bar 21 is:

so supported increased Wear on the inner regions of the lap sur-face will result until all four cont-act points 22,23, 24 and 25 effective to support the bar. Thereafter, the wear as between the inner and outer regions of the. lap surface is uniform, any tendency otherwise beingi instantly'and automatically corrected by a shifting of the dition is depicted in Fig. 7, wherein ring 32 is oflless height than ring 33, both'resting on a flat lapping sun-face .1 8. To compensate for the unequal heights, the contact points are adjusted up or down so that all four contact the upper surfaces G4-and 56 of the rings 32 and 33, re-

spectively. The establishment of contact between the cont-act points and the surfaces of the rings can be detected bythin feeler gages, by the use of chalk, or by any of the means normally used by a skilled machinist in a similar situation.

The application of the principle depicted in Figs, 4

to 7 inclusive to the machine of Fig. 1 isillustrated in Figs. 2 .and 3. As described above, the lap -11 vis a disc having an annular lapping surface 12 defined by inner." and outer peripheral edges 15 and 16. For purposes of illustration surface 12 is shown as being perfectly flat, but it is understood that surface 12 may be slightly convex or concave to produce complementary concave or convex surfaces, if desired. It is contemplated that surface 12 will be used to produce perfectly flat surfaceszon.

articles such as discs 13, and hence it is desirable to maintain the flatness of surface 35 as long as possible with the least attention on the partof the operator.

The'rneans for maintaining the flatness of lapping surface 12 comprises a plurality of conditioning rings 14 which, asshown in Fig. 1 may be four in number-a1.- r'anged in p.ai-rs,xeach pair'being disposed with its center on iadia-rneter; of the lapping surface, and each ring being: of an outsidediameter which is greater than the radial dim-ensionofsurface .12 so' that the ring overlaps the innerand outertperipheraledges 1'5 and 16, respectively,-

If the inequality is of surface 12. The upper surface 64 of each ring is recessed to form a shoulder 35 on which is mounted a pace 36 of an anti-friction bearing 87. The other race 88 supports a ring-like end 39 of a heavy, substantially rigid bar 40, the other end 41, as shown in Fig. 1 being likewise ring-like so that the bar is symmetrically formed with respect to the center of the lap. The opening 42 in each ring 14 is preferably smaller than the opening 43 in the end 39 of the bar, it being contemplated that the article 13 to be lapped will be inserted into ring 14 through said opening 43. Furthermore, since ring 14 rotates, whereas bar 40 does not, it is preferred that stationary end 39 should not touch any article within ring 14 which might be high enough to extend into opening 43.

Bar 40 is restrained from revolution with rings 1-4 and lapping surface 12 by lugs 44 formed on the ends of the bar which extend into U-shaped guides 45 secured to frame 10. Said guides are disposed to permit free vertical movement of bar 40 but to inhibit rotation of the bar relative to frame 10. It may be observed that since bar 40 may not move angularly relative to frame 10, the anti-friction bearing 37 will prevent ring 14 from moving angularly relative to frame lltl, although rotation of ring 14 about the axis of bearing 37 will be relatively unhindered.

The actual contact between end 39 of bar 40 and race 38 is established on one side by the end '46 of a bolt 47 which is threaded in an opening 48 in bar 40 disposed over race 38 on a diameter of lap 11. A nut 49 serves to lock bolt 47 in any desired position so that the distance which end 46 extends beyond the lower surface of bar 49 may be varied as desired. It is contemplated, however, that once an optimum position is determined, bolt 47 will remain in that position indefinitely. The side of ring 14 diametrically opposite bolt 47 is held down by an adjustable screw '50 having a knunled head 51, a graduated shank 52 and a rounded end '53 adapted to contact the top surface of race 38. A scale 54 secured to end 39 in proximity to shank 52 serves to 110- c-ate screw 50 relative to end 39 and with the graduations on shank 52 constitutes a micrometer scale. It is understood that the :outer contact points of bar ,0 will be similar to screw 50 and adjustable through a range of positions relative to ends 46 of the inner contacts from a position farther from lap surface 12 than ends 46 to a position closer to said surface 12. Thus, by adjusting the position of screws 50 before a lapping operation commences, one can make and maintain lapping surface 12 flat, convex or concave.

The corresponding bar for the conditioning rings dis posed on a diameter located at ninety degrees from the diameter on which bar 49 is located is identical to said bar 49, the crossing of the bars being effected preferably in a manner to avoid contact between the bars.

In operation, assuming that screws 50 and bolts 47 have been adjusted to define the desired surface, the articles to be lapped are placed within ring 14 and the lap lll is then rotated. The customary lapping compound is fed to lap surface 12 from a tank 57 (Fig. l) by any well known means such as by gravity along a wire 55. Bar 4'9, being held by lugs 44 in guides d5, will prevent the revolution of ring 14 with lapping surface 12 and hence ring 14 will rotate about the axis of bearing 37, thereby wearing lapping surface 12 while the article is being lapped. Any tendency for the lapping surface 12 to depart from the desired contour as edfined by contact points 46 and 53 will be immediately corrected by the transfer of the weight of bar 40 from the low region to the high region.

it may be observed that bar Ail? serves two purposes, first, as a means for automatically correcting any tendency of the lapping surface to deviate from the contour intended for it, and second, as a means for locating and holding a ring for rotation about its own axis at a predetermined position on the lap surface.

In place of two crossed bars, a single triangular weight (not shown) may be used, the ends of the weight being formed with openings similar to the open ends 39 of bars 40. Other configurationsof weights will suggest themselves to those skilled in the art, the guiding principle being rigidity in the weight, equal distribution of the weight among the rings, and the definition of the desired surface by the contact points. Other arrangements of antifriction bearings will also be apparent.

It is understood that the foregoing description is merely illustrative of a preferred embodiment of this invention and that the scope of this invention therefore is not limited thereto, but is to be determined by the appended claims.

I claim:

1. The method of conditioning a rotatable lap surface to coincide with a predetermined plane, said method com prising the steps of abrading the lap surface by means of a plurality of rotating rings each ring having substantially radially disposed sides, with one such side of each ring resting upon the lap surface whereby to abrade the lap surface by said side as aforesaid, said two rings being disposed on opposite sides of a lap diameter, placing a common rigid weight upon the other side of at least two of said rings while the rings are abrading the lap surface so as to support said weight by the rings with the center of gravity of the weight located substantially on the axis of rotation of the rotatable lap surface, and limiting the contact between the weight and rings to points which are in a plane parallel with the predetermined plane of the lap surface and on opposite sides of a diameter of each ring which is disposed transversely of a radius of the lap surface.

2. The method of conditioning a rotatable annular lap surface to coincide with a predetermined plane, said method comprising the steps of abrading the lap surface by means of a pair of rotating rings having substantially radially disposed sides each overlying radially inner and outer peripheral regions of the lap surface, with one side of each ring resting upon the lap surface, placing a common rigid weight upon the other side of the rings so as to support the weight by the rings, and establishing points of contact between the weight and each ring limited in location to the radially inner and outer peripheral regions of the lap surface, said points of contact being fixed in a plane parallel with the predetermined plane of the lap surface.

3. Apparatus for establishing a surface of predetermined contour upon a rotatable disc-like lap, comprising a plurality of rotating rings having substantially radially disposed sides and resting on said sides upon the surface of the lap, a common rigid weight supported by and bridging said rings, the center of gravity of said weight being disposed substantially in the axis of rotation of the lap, means for rotating the lap, and means limiting contact between the weight and rings to points lying in a plane parallel with the surface of predetermined contour and at opposite ends of a ring diameter which is parallel to a radius of the lap.

4. Apparatus for establishing a surface of predetermined conto-ur upon a disc-like rotatable lap, comprising a plurality of parallel'sided rings resting on their sides upon the operative surface of the lap, means for rotating the lap, said rings being substantially equiangularly spaced around the operative lap surface and substantially equidistantly spaced from the center of rotation of the opera tive lap surface, means for restraining said rings against revolution with the operative lap surface, a rigid weight supported by said rings, and means limiting contact between the weight and rings to points lying in a plane parallel with the surface of predetermined contour and disposed on opposite sides of a diameter of the rings transverse to a radius of the lap surface.

5. Apparatus for establishing a surface of predetermined contour as described in claim 3, said rings having openings, said weight having openings disposed over the openings in the rings, and said rings having lateral extensions to support the weight.

6.1Apparatus for establishing a surface of predetermined contour as described in claim 3, said rings having openings, said weight having openings disposed over the openings in' the rings, bearing means for the weight on the rings, means for restraining the rings against revolution with respect to the weight, and means for restraining the weight against revolution with the lap surface, said last-mentioned restraining means comprising a stationary frame, and interfitting means between the frame and weight restraining the weight and therefore the rings against rotary movement with the lap.

7. Apparatus for establishing a surface of predetermined contour as described in claim 3, said rings having openings, said weight having openings disposed over the openings in the rings, anti-friction bearing means for the rings on the'weight, and means for restraining the rings against revolution with the lap surface, said restraining means comprising a stationary frame, laterally extending lugs on the weight, U-shaped guides on the frame receiving the lugs and disposed to permit free vertical movement of the weight relative to the lap and means for restraining the rings against revolution with respect to the weight.

8. Apparatus for establishing a surface of predetermined contour as described in claim 3, and means for changing the vertical location of certain of the contact limiting means relative to the vertical location of the remaining contact limiting means to alter the plane defined by said contacts and thereby to alter the contour of the lap surface.

9. Apparatus for establishing a surface of predetermined contour upon a rotatable circular lap surface comprising a plurality of rotating rings resting on their sides U (3 uponthe surface, said rings having parallel sides and beingdisposed on opposite sides of the center of the lap surface with their centers on a diameter of the lap-surface, anda weighted beam extending across said rings, the axis ofthe beam lying substantially upon the said diameter of the lap surface and the weight of the beam' being symmetrically disposed with respect to the center of the lap surface, and means limiting contact between the beam and rings to points lying in a plane parallel with the surface of predetermined contour.

10. Apparatus as described in claim 9, and bearing means on the beam for rotatably holding the rings therein.

11. Apparatus, as described in claim 9, bearing means on the beam for rotatably holding the rings therein, a stationary frame, and interfitting means on the frame and beam for holding the beam and the rings rotatably held therein against revolution with the lap.

12. Apparatus as described in claim 9, said beam having rings on the ends thereof disposed concentrically with respect to two of the rotating rings, said rotatingrings having openings therein, the openings inthe beam rings being at least equal in diameter to the internal diameter of the said two rotating rings, whereby articles to be lapped may be inserted into the rotating rings through the beam rings.

References Cited in the file of this patent UNITED STATES PATENTS 453,566 Schefold June 2, 1891 460,632 Delrue Oct. 6, 1891 2,391,388 Bullard Dec. 23, 1945 2,407,206 Luboshez Sept. 3, 1946 2,653,422 Koshong Sept. 29, 1953 

